APPLIED/Cmnt: [SRU][Focal][PATCHv2] s390/ptrace: return -ENOSYS when invalid syscall is supplied

[Stefan Bader]

On 15.12.20 18:35, Dan Streetman wrote:
> From: Sven Schnelle <svens at linux.ibm.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1895132
> 
> The current code returns the syscall number which an invalid
> syscall number is supplied and tracing is enabled. This makes
> the strace testsuite fail.
> 
> Signed-off-by: Sven Schnelle <svens at linux.ibm.com>
> Signed-off-by: Vasily Gorbik <gor at linux.ibm.com>
> (backported from commit cd29fa798001075a554b978df3a64e6656c25794)
> Signed-off-by: Dan Streetman <ddstreet at canonical.com>
> 
> ---

Applied to focal:linux/master-next. Thanks. Btw, this was likely buried by the
fact that the v2 was sent as a reply to the original v1 submission.  I hope that
shows why this is a bad idea.

-Stefan

> changes since v1: removed return before added goto
> 
>  arch/s390/kernel/ptrace.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
> index c6aef2ecf289..ad74472ce967 100644
> --- a/arch/s390/kernel/ptrace.c
> +++ b/arch/s390/kernel/ptrace.c
> @@ -867,6 +867,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
>  asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
>  {
>  	unsigned long mask = -1UL;
> +	long ret = -1;
>  
>  	/*
>  	 * The sysc_tracesys code in entry.S stored the system
> @@ -878,27 +879,33 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
>  		 * Tracing decided this syscall should not happen. Skip
>  		 * the system call and the system call restart handling.
>  		 */
> -		clear_pt_regs_flag(regs, PIF_SYSCALL);
> -		return -1;
> +		goto skip;
>  	}
>  
>  	/* Do the secure computing check after ptrace. */
>  	if (secure_computing(NULL)) {
>  		/* seccomp failures shouldn't expose any additional code. */
> -		return -1;
> +		goto skip;
>  	}
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
> -		trace_sys_enter(regs, regs->gprs[2]);
> +		trace_sys_enter(regs, regs->int_code & 0xffff);
>  
>  	if (is_compat_task())
>  		mask = 0xffffffff;
>  
> -	audit_syscall_entry(regs->gprs[2], regs->orig_gpr2 & mask,
> +	audit_syscall_entry(regs->int_code & 0xffff, regs->orig_gpr2 & mask,
>  			    regs->gprs[3] &mask, regs->gprs[4] &mask,
>  			    regs->gprs[5] &mask);
>  
> +	if ((signed long)regs->gprs[2] >= NR_syscalls) {
> +		regs->gprs[2] = -ENOSYS;
> +		ret = -ENOSYS;
> +	}
>  	return regs->gprs[2];
> +skip:
> +	clear_pt_regs_flag(regs, PIF_SYSCALL);
> +	return ret;
>  }
>  
>  asmlinkage void do_syscall_trace_exit(struct pt_regs *regs)
> 


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